Whales, their babble, and clan dialects.
Shane Gero, Hal Whitehead and Luke Rendell of the Universities of Aarhus, (Denmark) Dalhousie (in Halifax, Nova Scotia) and St Andrews (Scotland) present us with the role of complex social structure in transmitting a repertoire of calls in sperm whales. The culturally transmitted dialects of their signals confer on the whales a language of
codas (signals transmitted across vast distances acoustically.)
9 social units of Physeter macrocephalus living in the Caribbean were studied for 6 years, to discover the extent to which codas were different or shared. As an extra, the study hoped to investigate whether the complexity of social structure could drive the evolution of an advanced communication system. Birds, bats, monkeys and mustelids (such as the mongoose, stoat and weasel) have been investigated in similar ways. The theory is that more complicated signalling would evolve as any society found a need for more social interaction.
Whales have had the ocean as an acoustic challenge in which to develop systems that suited their own advanced social groupings. Human ancestors performed in such advanced groups on the savannah. Then, social signalling on land proved immensely valuable between
teams of vocal, visual, tactile and even olfactory animals. The ocean habitat provided vast expanse, especially for sound transmission, while behavioural patterns might have varied among some groups depending on the local ecologies. The sperm whale has possibly the largest cooperative group ethic outside of our own species, especially among the hierarchies of females in the matrilineal groups.
Three or more broadband clicks function as a single coda for the groups, carried out as duets in which the 2 whales overlap and repeat the signals, most often when they are at or near the surface. Vocal clans of thousands of individuals exist with similar dialects. The Pacific cultural approach is to ignore those with different dialect, while in the Atlantic, the repertoire used in one area is apparently always the same. A great number of diverse calls also signify that it is not only social structure that is being communicated, but a burgeoning dataset of aquatic chat that was expertly built up during this research, communicating who knows what!
Dominicas west coast proved to be a useful base for both whales and researchers over the winters of 2005-2010. From the very first recordings of echolocation clicks from a single whale diving to multiple whales in clusters as they began to dive and the surface recorded codas, sound records extended over 7 of the groups for more than one year. With an average of 8 individuals and at least one calf in each, the groups produced 4,116 codas, during 164 recordings.
21 types of coda were found, each often consisting of 4-5 clicks, many of which were used exclusively by individuals.2 or more codas were used by each group for more than 10% of the time. Significantly, no group repertoire changed over time, certainly over the 6 years of the study. Each individual had his or her own repertoire, while sharing at least 2 codas between the members of their unit. Younger animals (mean:4.9 types had more codas than older ones (mean 8.6 types,) presumably specifically
Overall, the hypothesis that social complexity drives greater communication skills is upheld by the investigation. Now we have this theory working among marine mammals, as opposed to the land animals in which it has already been shown. All the units studied around the west of Dominica belong to one whale clan, according to findings in the Pacific. The researchers could identify each whale from acoustic clues while Identification signals between whales could be said to have also provided ID, but the proof is hard to find. We know little of how the whale could detect small nuances of meaning form a position, just part of a coda or even past knowledge of others and their surroundings. Valuable research can now continue of how the coda develops through social learning.
Babbling of infants develops into an exact adult set of utterances, according to work on one calf. But whether humans and songbirds learn in a similar way is to be researched among clans of the elusive whales diving to those incredible depths in the Pacific or elsewhere in the Atlantic.
The work was published today in Royal Society Open Science as
Individual, unit and vocal clan level identity cues in sperm whale codas. We caught some of the earlier discoveries of this research in Dominica way back in 2011, with this piece of research on Sperm whales speak with regional accents.